Be able to utilize homeserver.yaml for any and all s3_media_upload configuration settings

[ShadowJonathan]

Is your feature request related to a problem? Please describe. Currently the s3_media_upload tool requires:

1. database.yaml with an abridged snippet of database configuration.
2. Extra configuration parameters when uploading files
3. ~/aws/config for implicitly supplying all other parameters.

Describe the solution you'd like Be able to extract the required information from a homeserver.yaml reference, pointing the tool to find and utilize those parameters to do an completely automated and smooth transfer.